[PATCH nft,v2 5/7] mnl: estimate receiver buffer size

[Pablo Neira Ayuso <pablo@netfilter.org>]

Set a receiver buffer size based on the number of commands and the
average message size, this is useful for the --echo option in order to
avoid ENOBUFS errors.

Double the estimated size is used to ensure enough receiver buffer
space.

Skip buffer receiver logic if estimation is smaller than current buffer.

Reported-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/mnl.h     |  3 ++-
 src/libnftables.c |  5 +++--
 src/mnl.c         | 11 ++++++++---
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/include/mnl.h b/include/mnl.h
index c63a7e7fd73a..9f50c3da0f3a 100644
--- a/include/mnl.h
+++ b/include/mnl.h
@@ -25,7 +25,8 @@ bool mnl_batch_ready(struct nftnl_batch *batch);
 void mnl_batch_reset(struct nftnl_batch *batch);
 uint32_t mnl_batch_begin(struct nftnl_batch *batch, uint32_t seqnum);
 void mnl_batch_end(struct nftnl_batch *batch, uint32_t seqnum);
-int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list);
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
+		   uint32_t num_cmds);
 
 int mnl_nft_rule_add(struct netlink_ctx *ctx, const struct cmd *cmd,
 		     unsigned int flags);
diff --git a/src/libnftables.c b/src/libnftables.c
index 199dbc97b801..a58b8ca9dcf6 100644
--- a/src/libnftables.c
+++ b/src/libnftables.c
@@ -21,7 +21,7 @@ static int nft_netlink(struct nft_ctx *nft,
 		       struct list_head *cmds, struct list_head *msgs,
 		       struct mnl_socket *nf_sock)
 {
-	uint32_t batch_seqnum, seqnum = 0;
+	uint32_t batch_seqnum, seqnum = 0, num_cmds = 0;
 	struct nftnl_batch *batch;
 	struct netlink_ctx ctx;
 	struct cmd *cmd;
@@ -49,6 +49,7 @@ static int nft_netlink(struct nft_ctx *nft,
 					 strerror(errno));
 			goto out;
 		}
+		num_cmds++;
 	}
 	if (!nft->check)
 		mnl_batch_end(batch, mnl_seqnum_alloc(&seqnum));
@@ -56,7 +57,7 @@ static int nft_netlink(struct nft_ctx *nft,
 	if (!mnl_batch_ready(batch))
 		goto out;
 
-	ret = mnl_batch_talk(&ctx, &err_list);
+	ret = mnl_batch_talk(&ctx, &err_list, num_cmds);
 
 	list_for_each_entry_safe(err, tmp, &err_list, head) {
 		list_for_each_entry(cmd, cmds, list) {
diff --git a/src/mnl.c b/src/mnl.c
index 6c85b1855c86..96984f03e1be 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -295,12 +295,14 @@ static ssize_t mnl_nft_socket_sendmsg(struct netlink_ctx *ctx,
 	return sendmsg(mnl_socket_get_fd(ctx->nft->nf_sock), msg, 0);
 }
 
-int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
+int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list,
+		   uint32_t num_cmds)
 {
 	struct mnl_socket *nl = ctx->nft->nf_sock;
 	int ret, fd = mnl_socket_get_fd(nl), portid = mnl_socket_get_portid(nl);
 	uint32_t iov_len = nftnl_batch_iovec_len(ctx->batch);
 	char rcv_buf[MNL_SOCKET_BUFFER_SIZE];
+	size_t avg_msg_size, batch_size;
 	const struct sockaddr_nl snl = {
 		.nl_family = AF_NETLINK
 	};
@@ -308,14 +310,17 @@ int mnl_batch_talk(struct netlink_ctx *ctx, struct list_head *err_list)
 		.tv_sec		= 0,
 		.tv_usec	= 0
 	};
-	fd_set readfds;
 	struct iovec iov[iov_len];
 	struct msghdr msg = {};
+	fd_set readfds;
 	int err = 0;
 
 	mnl_set_sndbuffer(ctx->nft->nf_sock, ctx->batch);
 
-	mnl_nft_batch_to_msg(ctx, &msg, &snl, iov, iov_len);
+	batch_size = mnl_nft_batch_to_msg(ctx, &msg, &snl, iov, iov_len);
+	avg_msg_size = div_round_up(batch_size, num_cmds);
+
+	mnl_set_rcvbuffer(ctx->nft->nf_sock, num_cmds * avg_msg_size * 2);
 
 	ret = mnl_nft_socket_sendmsg(ctx, &msg);
 	if (ret == -1)
-- 
2.11.0